1. Field of the Invention
The present invention relates to a cam follower with roller, and more particularly, to a cam follower with roller that is incorporated into a valve mechanism of an internal combustion engine of a vehicle.
2. Description of the Background Art
To increase durability and maintenability of an engine valve system, it is necessary to address the problems related to abrasion and insufficient lubrication of a cam and a follower on a cam shaft.
To prevent abrasion of the valve system, a hydraulic lash adjuster has been practically utilized in an OHV-type engine, and recently, use of a rolling bearing for the follower has rapidly increased in order to reduce abrasion and friction loss of the cam and follower.
A cam is a portion where lubrication easily dies away among other engine components, and a contact surface thereof is called a boundary lubrication area. In a cam follower with roller used under such circumstances, the cam is in contact with the roller basically by rolling contact. However, the rolling contact involves sliding, since absolute rolling movement is hindered by abrupt variations in the load applied onto the roller and by changes in the rolling speed of the roller due to the shape of the cam. Thus, peeling or smearing, i.e. surface damage, occurs on an outer diameter rolling surface of the roller in connection with the lubricating conditions (amount and temperature of oil, debris) and surface roughness of the opposing cam, resulting in a short life.
Moreover, a supporting shaft rotatably supporting the roller is limited in the loaded zone, and thus a very large pressure is applied onto the surface of the supporting shaft, resulting in shorter rolling fatigue life compared to that of the roller or a bearing. Therefore, increase of rolling fatigue life has been desired.
The bearing rotatably supporting the roller is generally a full type roller bearing, which generates skew and relative sliding, so that the bearing is also subjected to surface damage such as peeling and smearing.
It is noted that SUJ2 has conventionally been used for the material of such roller, supporting shaft and bearing.
An object of the present invention is to provide a cam follower with roller having a roller, a supporting shaft rotatably supporting the roller and a rolling element that are made of heat-resisting, peeling-resisting and smearing-resisting materials, and capable of increasing rolling fatigue life and reducing surface damage under high temperature conditions.
According to the present invention, in a cam follower with roller including a cam follower body having a roller supporting portion integrated into the cam follower body, a supporting shaft of which both ends are fixed to the roller supporting portion, and a roller rotatably supported on the supporting shaft with a plurality of needle rollers interposed; at least one of the supporting shaft, needle roller and roller is formed of heat-resisting steel.
According to a cam follower with roller of the present invention, at least one of the supporting shaft, needle roller and roller is formed of the heat-resisting steel, so that the heat resistance can be improved and surface damage such as smearing and peeling can be prevented, resulting in increase of rolling fatigue life under high temperature conditions.
In the cam follower with roller, preferably, the both ends of the supporting shaft is caulked to be fixed to the roller supporting portion.
Thus, the both ends of the supporting shaft are caulked to be fixed to the roller supporting portion, and this caulking and fixing work can be performed merely by notching an end surface of the supporting shaft. Therefore, no impact is applied onto the roller supporting portion, so that the cam follower would not be deformed at assembling.
In the cam follower with roller, preferably, a rolling contact surface on which the needle roller rolls, of an outer circumferential surface of the supporting shaft, is subjected to high frequency quenching so as to have a surface hardness of at least HV 650, and the both ends of the supporting shaft is subjected to no quenching so as to have a surface hardness of at least HV 200 and at most HV 280.
Since the rolling contact surface has a surface hardness of at least HV 650, it can remain intact when the needle roller rolls, without the supporting shaft being deformed due to abrasion. Furthermore, both end surfaces of the supporting shaft has a surface hardness in the range between HV 200 and HV 280, so that the end surfaces can be notched at assembling to enlarge the edge portion. Such a caulking process generates no crack at the ends, allowing the supporting shaft to be easily and firmly fixed to the cam follower body.
In the cam follower with roller, preferably, the supporting shaft is through-quenched and is press-fit to the roller supporting portion.
Thus, the supporting shaft is through-quenched, allowing the hardness to be higher. Furthermore, the supporting shaft is press-fit to the roller supporting portion, so that the supporting shaft can be fixed to the roller supporting portion even if the supporting shaft is produced by the through quenching which allows no caulking for fixing.
In the cam follower with roller, preferably, the supporting shaft is through-quenched and is fixed to the roller supporting portion in the axial direction of the supporting shaft with a snap ring interposed.
Thus, the supporting shaft is through-quenched, allowing the hardness to be higher. Furthermore, the supporting shaft is fixed by the snap ring, so that the supporting shaft can be fixed to the roller supporting portion without press-fitting or caulking work.
In the cam follower with roller, preferably, the roller is made of heat-resisting steel.
In particular, the roller is in rolling-contact with the cam while sliding, and thus the sliding or tangential stress may act onto the roller to increase the temperature on the roller surface, or shear heating occurs in lubrication oil to reduce the thickness of an oil film. This may easily cause surface damage such as peeling and smearing. Such surface damage can, however, be prevented by using the heat-resisting steel for the roller.
In the cam follower with roller, preferably, the heat-resistant steel is made of a steel material at least containing as alloy elements in a matrix, by mass %, at least 0.6% and at most 1.3% of C(carbon), at least 0.3% and at most 3.0% of Si(silicon), at least 0.2% and at most 1.5% of Mn(manganese), at most 0.03% of P(phosphorus), at most 0.03% of S(sulfur), at least 0.3% and at most 5.0% of Cr(chromium), at least 0.1% and at most 3.0% of Ni(nickel), at most 0.050% of Al(aluminum), at most 0.003% of Ti(titanium), at most 0.0015% of O(oxygen) and at most 0.015% of N(nitrogen), and a remaining part of Fe(iron) and an unavoidable impurity.
The use of the steel material allows rolling fatigue life to be elongated by quenching and tempering, under the environment contaminated with debris, without a carbonitriding process. Thus, carbonitriding can be dispensed with, reducing the manufacturing cost. Moreover, the steel material is superior in its heat resistance, peeling-resisting property and smearing-resisting property, so that rolling fatigue life can be increased and surface damage can be reduced under high temperature conditions.
The reasons for limitations of each component indicated above will be described below.
(1) C Content (at Least 0.6% and at Most 1.3%)
C is a requisite element for securing the strength as a rolling bearing, and at least 0.6% of the C content is required to maintain the hardness after a prescribed heat treatment. Thus, the lower limit of the C content is set to be 0.6%. Moreover, if the content of C exceeds 1.3%, large carbide appears, resulting in shorter rolling fatigue life. Therefore, the upper limit of the C content is set to be 1.3%.
(2) Si Content (at Least 0.3% and at Most 3.0%)
Si is preferably added because it has a function of suppressing softening in a high temperature range and improving heat resistance of the rolling bearing. When Si content is less than 0.3%, such effect cannot be attained. Therefore, the lower limit of the Si content is set to be 0.3%. As the Si content increases, heat resistance also improves. The effect, however, is saturated when the Si content is added exceeding 3.0%, while susceptibility to hot working and machinability are degraded. Therefore, the upper limit of the Si content is set to be 3.0%.
(3) Mn Content (at Least 0.2% and at Most 1.5%)
Mn is an element used for deoxidation in manufacturing of steel, and at the same time, is an element that improves a quenching property. In order to obtain such effects, it is necessary to add Mn by at least 0.2%. Thus, the lower limit of the Mn content is set to be 0.2%. When the content exceeds 1.5%, however, machinability degrades significantly. Therefore, the upper limit of the Mn content is set to be 1.5%.
(4) P Content (at Most 0.03%)
P is segregated at austenite grain boundary of the steel, causing degradation of toughness and rolling fatigue life. Therefore, the upper limit of the content is set to be 0.03%.
(5) S Content (at Most 0.03%)
S hinders susceptibility of steel to hot working and forms a non-metallic inclusion in the steel, degrading toughness and rolling fatigue life. Therefore, the upper limit of the S content is set to be 0.03%. Moreover, though S is disadvantageous in the aspect described above, it has an effect of improving machinability. Therefore, though much smaller content of S is desirable, addition of S may be allowed within the range of up to 0.005%.
(6) Cr Content (at Least 0.3% and at Most 5.0%)
Cr serves an important role in this alloy composition and is added to improve the quenching property, to ensure the hardness due to the carbide, and to elongate lifetime. In order to obtain prescribed carbide, it is necessary to add at least 0.3% of the Cr content, and therefore the lower limit of the Cr content is set to be 0.3%. However, when the content exceeds 5.0%, large carbide appears, degrading rolling fatigue life. Therefore, the upper limit of the Cr content is set to be 5.0%.
(7) Al Content (at Most 0.050%)
Al is used as a deoxidizer at manufacturing of steel. However, the content thereof is preferably reduced, since Al generates a hard oxide-based inclusion, degrading rolling fatigue life. Further, a large amount of Al exceeding 0.050% would significantly deteriorate rolling fatigue life. Therefore, the upper limit of the Al content is set to 0.050%.
It is noted that less than 0.005% of the Al content would raise the manufacturing cost of steel, and thus the lower limit of the Al content is preferably set to 0.005%.
(8) Ti Content (at Most 0.003%); O Content (at Most 0.0015%); and N content (at most 0.015%)
Ti, O and N form oxide and nitride in the steel, and serve as non-metallic inclusions that would be sources of fatigue fracturing, to degrade rolling fatigue life. Therefore, the upper limits of the elements are respectively set as follows: 0.003% for Ti, 0.0015% for O and 0.015% for N.
(9) Ni Content (at Least 0.1% and at Most 3.0%)
Ni is an element serving an important role in the present invention. In particular, Ni suppresses change in the structure during the process of rolling fatigue when used in a high temperature environment, and has the effect of preventing deterioration of hardness in a high temperature range and elongating rolling fatigue life. In addition, Ni is also effective at improving toughness and elongating lifetime under a debris contamination environment, while improving corrosion resistance. In order to attain such effects, at least 0.1% of the Ni content is required, and thus the lower limit of the Ni content is set to be 0.1%. When the content exceeds 3.0%, however, a large amount of retained austenite is generated at the time of quenching, making it difficult to attain a prescribed hardness and, in addition, the cost of the steel material increases. Therefore, the upper limit of the Ni content is set to be 3.0%.
In the cam follower with roller, preferably, the steel material is formed by one of quenching and carburizing processes followed by a tempering process.
Each component of the cam follower with roller used in a high-temperature range as in the present invention is subjected to the tempering process at a temperature equal to or higher than an environment temperature, in order to stabilize the size of each component under the environment of use.
In the cam follower with roller, preferably, an effective hardened portion with a hardness of at least HV 550 has a depth of at least 1.0 mm, in a rolling contact surface on which the needle roller rolls, of an outer circumferential surface of the supporting shaft.
Thus, a sufficient hardness can be attained for the surface on which the needle roller rolls.
In the cam follower with roller, preferably, the supporting shaft is made of the heat-resistant steel.
This limits a loaded zone, and a very large pressure is applied on the surface, so that rolling fatigue life can be increased even in the supporting shaft having a strict condition of rolling fatigue life.
In the cam follower with roller, preferably, the needle roller is made of the heat-resistant steel, is quenched and hardened to a core, and has a surface hardness of at least HV 650.
This allows the peeling-resistant property and smearing-resistant property to be improved even in the needle roller at which skew and relative sliding occurrs at the time of rolling.
In the cam follower with roller, preferably, the roller is quenched and hardened to a core, and has a surface hardness of at least HV 650.
This can assure a sufficient hardness in rolling.
In the cam follower with roller, preferably, an infinite number of microscopic concave recesses are randomly formed on an outer surface of the roller. When surface roughness of the outer surface of the roller obtained in each of axial and circumferential directions is indicated by a parameter RMS, a ratio (RMS(L)/RMS(C)) of axial surface roughness RMS(L) to circunferential surface roughness RMS(C) is at most 1.0, and a parameter SK value of the surface roughness is at most xe2x88x921.6.
Thus, even under a condition in which roughness is inferior on the finished surface of the opposing cam, an excellent ability of forming an oil film can be attained so that a sufficient thickness of the oil film can be secured, and therefore, the rolling contact portion can be prevented, as much as possible, from being in contact with metal. Furthermore, the surface of the rolling contact portion that is in contact with metal is reduced, so that the outer diameter of the cam follower can be free from surface damage, peeling and smearing, as well as unusual abrasion and separation therefrom. Therefore, durability can be increased.